The present disclosure is directed to systems and methods of making and using prosthesis. More particularly, the present disclosure relates to systems and methods of making and using multi-axial powered ankle-foot prosthesis.
Walking in a straight line requires complex modulation of a person's muscle contractions to control the stiffness of the person's ankle and to generate forward propulsion. Similar muscle contractions are required to generate the appropriate ground reaction forces to steer the body while turning.
People having amputations below the knee who use passive prosthesis have been found to expend 20-30% more energy than non-amputees to walk at an equivalent speed. The increase in energy expenditure results in a preferred walking speed which is 30-40% slower than non-amputees. Powered prostheses have been developed to reduce the metabolic cost during straight walk by providing energy to the gait at push-off.
Ankle-foot prostheses provide locomotion assistance to amputees, emulating the function of the healthy ankle. Quasi-static impedance (stiffness) and mechanical impedance of the ankle in the sagittal plane have been used in the design of ankle-foot prostheses to allow for the production of positive work during gait. Conventional, commercially available, prosthetics have been designed to actively control one degree of freedom in the sagittal plane. For example, some have developed a knee and ankle prosthesis capable of controlling the impedance of both the knee and ankle joints in the sagittal plane by controlling the neutral position of the foot during gait. Systems available from BiOM provide the energy during plantarflexion, actively contributing in gait and lowering metabolic cost. The controller in BiOM systems allow for gait in different cadence over surfaces with different inclinations. The Proprio Foot from Ossur uses a stepper motor to provide dorsiflexion motion during swing forward, as well as adjustment of the ankle angle on the surface with different terrains. A controller used with Ossur uses a pattern recognition algorithm to continuously adapt to the user's gait. As another example, Elan from Endolite uses a hydraulic ankle, and the controller provides for foot clearance and plantarflexion for support during stance by adjusting the ankle joint resistance. While the aforementioned prostheses improve the gait of amputees, they are designed to modulate the ankle torques in the sagittal plane only.
In addition, the focus of powered prosthesis has been on increased mobility in forward locomotion. However, studies show that in average, 25 percent of an average person's steps have been found to be turning steps. Two different strategies are commonly used for turning. Spin turn requires the person to turn the body around the leading leg. For example, the person may turn right with right leg in front. Step-turn requires the person to shift their body weight to the leading leg while simultaneously stepping the opposite leg in. The step-turn has shown to allow for increased stability when turning.
It has been shown that the velocity, length, and width of a step-turn are considerably different than the straight walk. Additionally, turning requires modulation of the ankles impedance in both Dorsiflexion-Platarflexion (DP) and Inversion-Eversion (IE) planes to control the lateral and forward reaction forces to maintain the person's center of mass along the desired trajectory. Therefore, the ground reaction forces exhibited during a step-turn are greater than those experienced during a straight walk.
Due to the lack of appropriate propulsion provided by passive prostheses, amputees rely on different gait strategies than non-amputees. Non-amputees have been found to rely mainly on their ankle rotation in the sagittal plane and hip rotations in the coronal plane when turning. Conversely, amputees rely on their hip rotations in both the sagittal plane and the coronal plane when turning. Consequently, energy consumption during each step is significantly higher for an individual with a conventional transtibial prosthetic. The energy consumption required at each step in an average able-bodied human weight 70 kg is between 36 J/step for walking and up to 100 J/step for running. Energy consumption for an individual having a conventional prosthetic may increase by as much as 35%.
When physical systems interact with each other, they behave either as an impedance or an admittance. A system that behaves as an impedance accepts external motion inputs and generates force outputs. Systems that behave as an admittance accept external force inputs and generate motion outputs. Coupled mechanical systems must physically complement each other, meaning that in any degree of freedom, if one system is an admittance, the opposing system must be an impedance.
During gait, at the moment the heel interacts with the ground, also referred to as “heel-strike”, the ankle accepts the external force and generates the appropriate motion, so it may be considered a system in admittance. Conversely, at push-off the ankle generates the necessary torques to produce a desired motion, and may therefore be considered as a system an impedance.
Therefore, further development of prosthesis is needed to provide amputees with more efficient and effective movements that more accurately approximate the function of natural limbs.